This invention relates generally to machine tools, and particularly to those of the type having a spindle to which various cutting tools, arbors and other attachments may be interchangeably mounted. More particularly, the invention pertains to a spindlehead featuring a mechanism for feeding the spindle against work. The spindlehead according to the invention is well suited for use in boring machines, although no unnecessary limitations thereto are intended.
The spindle of boring machines is fed longitudinally out of the spindlehead against work. Take, for example, a horizontal boring and milling machine for a study of the conventional spindle feed mechanism. The boring spindle has been received within a hollow milling spindle and keyed or splined thereto for axial sliding movement relative to the same. A feed mechanism such as that comprising a hydraulic actuator or a feed screw has been coupled to the boring spindle for axially driving the same with respect to the milling spindle. The milling spindle has been revolved as by a gear train coupled to a drive motor for the boring spindle.
Thus, according to the prior art, the boring spindle has been fed out of the milling spindle during machining. It will therefore be understood that the boring spindle has been supported essentially in a cantilever fashion when extended out of the milling spindle. Such cantilever support of the boring spindle is of course objectionable because it is subjected to greater bending stresses from the cutting tool mounted to its distal end, during machining. The results have been the easy deflection of the boring spindle under load and the consequent vibration of the cutting tool. The boring spindle has been easy to deflect under its own weight, too, so that limitations have been imposed on the size and weight of cutting tools and attachments that can be mounted to the spindle.
An additional inconvenience has manifested itself from the fact that, being slidable axially with respect to the milling spindle, the boring spindle has been free to undergo axial deformation. As heat develops during machining, the boring spindle has been susceptible to thermal deflection, adversely affecting the accuracy of machining.